Perturbations in hormone levels, growth, body habitus, and behavior are generally believed to be related during human puberty. The present proposal will attempt to determine the direct influence of sex hormones on behavior by performing sequential behavior testing in 55 sex-steroid- deficient adolescents before, during and after they receive therapeutic hormone replacement therapy. Boys and girls with primary or secondary hypogonadism have received three dose levels of intramuscular testosterone enanthate (boys) or oral conjugated estrogen (girls) alternating with placebo over 3-month periods. The study design is randomized, double-blind placebo controlled cross-over clinical trial. To assess longer term behavioral effects of sex steroids, subjects are being retested 12-18 months after completion of the initial 21 month protocol.